1. Field of the Invention
The present invention relates to a sampling needle and a sample injection apparatus for temporarily storing a sample and supplying the sample to a predetermined receiving unit.
2. Description of the Related Art
A liquid chromatography apparatus is widely used as chemical analyzing means for separating and determining the quantity of a chemical substance. FIG.1 is a diagram showing a basic configuration of a liquid chromatography apparatus.
The liquid chromatography apparatus shown in this drawing includes a mobile phase reservoir 101 for storing liquid corresponding to a mobile phase, a mobile phase degassing unit 102 for removing air from the liquid (mobile phase), a pump 103 for sending the liquid (mobile phase) from the mobile phase reservoir 101 to a detector 107, an (auto) sample injection apparatus 104 for injecting a sample into the liquid (mobile phase) that is moving toward a separation column 105, the separation column 105 that is filled with a packing material for separating components of the sample, a column oven 106 for maintaining the separation column 105 at a substantially constant temperature, and the detector 107 that detects diffused components of the sample, for example.
In recent years and continuing, improvements in detection sensitivity of liquid chromatography are in demand, and in turn, measures are being implemented to increase the sensitivity of the liquid chromatography apparatus. However, as the sensitivity of the liquid chromatography apparatus is increased, the so-called carry-over becomes a problem.
Carry-over refers to an effect in which a substance of a sample previously measured remains in the liquid chromatography apparatus so that the remaining substance is detected in a current measurement, thereby falsely indicating that it is a component of the sample currently being measured. Such an effect may degrade the reliability of the analysis result. When a sample is injected into a liquid corresponding to the mobile phase by the auto sample injection apparatus 104, the sample may remain in the auto sample injection apparatus 104. The remaining sample may be introduced into the liquid chromatography analyzing system when a next sample is injected, and in this way carry-over may occur.
The occurrence of carry-over may be reduced by removing the sample remaining in the auto sample injection apparatus 104. In turn, research is being conducted to determine the position at which the sample remains within the auto sample injection apparatus 104.
In the auto sample injection apparatus 104, a sampling needle 110 (see FIG.2) extracts a sample from a sample solution supplied in a sample container, and the sampling needle 110 extracting this sample is inserted into an injection port of an injection valve so that the sample inserted into the injection port may be transported to the separation column 105 by a flow path switching operation performed by the injection valve.
The outer wall of the sampling needle 110, the injection port into which the sample is injected, and the flow path of the sample within the injection valve may be examples of locations at which the sample may remain within the auto sample injection apparatus 104. In turn, for example, Japanese Laid-Open Patent Publication No. 11-304779 discloses a technique for cleaning a portion or all of the locations at which the sample may remain within the auto sample injection apparatus so as to reduce the occurrence of carry-over.
The inventors of the present invention performed the following test using a liquid chromatography apparatus including the auto sample injection apparatus 104. First, a sample solution was injected into the liquid chromatography apparatus and a detection process was performed. Then, a cleaning process was performed on all the locations at which the sample may remain within the sample injection apparatus 104. Then, a blank sample solution (mobile phase) was injected using the auto sample injection apparatus 104 and a determination was made as to whether traces of the first sample solution remaining within the auto sample injection apparatus 104 could be found.
FIG. 4 shows a chromatogram obtained from performing the above test. As can be appreciated from this drawing, even when a cleaning process was performed on all locations at which the sample may remain within the sample injection apparatus 104, a carry-over peak occurred as is indicated by the arrow X in the drawing. Therefore, a more reliable method for preventing carry-over is required.